He gained the rank of Lieutenant in the 10th Battalion, Middlesex Regiment, but never fought in the First World War owing to ill health. His subsequent advocacy of pacifism during the 1930s, and his attempt to mediate a truce in the Second World War by visiting the German legation in Dublin, led to his name being placed on a list of persons to be arrested in the event of a German invasion [1]. He went on to be patron of the British People's Party based in Covent Garden, an anti-war party that was accused of having fascist sympathies. Despite this, he contributed articles on Social Credit and pacifism to Guy Aldred's journal, The Word, between 1940 and his death. He was also an ornithologist, specialising in parrots and budgerigars, to whom he would feed chocolates, although his eldest son was often reduced to eating them; his other pets included a spider to whom, according to Nancy Mitford's The English Aristocracy, he would regularly feed roast beef and Yorkshire pudding. His cohort included John Beckett, a former Labour Member of Parliament whom other fascist groups complained siphoned away his monies, which could have been spent on more worthy causes.

While known as the Marquess of Tavistock, he wrote "Parrots and Parrot-like Birds". He was a founder member and first President of the Foreign Bird League. He was successful in breeding many species, including the Tahiti Blue Lorikeet and Ultramarine Lorikeet. Both of these are recognised as the world's first breedings in captivity. The Marquess disposed of his birds upon succeeding to the Dukedom in 1939.

He died in 1953, aged 64, as a result of a gunshot wound in the grounds of his Endsleigh estate in Devon. The coroner recorded his death as accidentally inflicted, but his elder son suggested it may have been deliberately self-inflicted,.

Hastings Russell features largely in his son John Ian's memoir, A Silver-Plated Spoon (World Books, 1959). He is described as "The loneliest man I ever knew, incapable of giving or receiving love, utterly self-centred and opinionated. He loved birds, animals, peace, monetary reform, the park and religion." In conjunction with his father, Hastings Russell managed to tie up the family fortunes in a way that made it extremely difficult for his son and heir to access the property.